1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an electrophotographic color image forming apparatus with a plurality of developing units.
2. Description of the Related Art
Generally, in a color image forming apparatus using electrophotography, an electrostatic latent image is formed on a photoconductor charged with a uniform potential by applying light to the charged photoconductor. The electrostatic latent image on the photoconductor is developed into a toner image using color toner, and the toner image is transferred and fused to a paper sheet to form a color image on the paper. The electrophotographic color image forming apparatus generally uses yellow (Y), magenta (M), cyan (C), and black (K) toner to form a color image. Therefore, to attach the four toner colors to the electrostatic latent image, the electrophotographic color image forming apparatus requires four developing units that respectively contain the four toner colors. For this reason, the color image forming apparatus is larger than a monochrome image forming apparatus. Also, when toner is used up, the developing unit is entirely replaced with a new one. Though the developing unit contains toner for printing images on several thousand printing media, other parts of the developing unit, such as a developer roller, can be used for printing images on several tens of thousands of printing media. Therefore, replacing the entire developing unit is not economical.
Accordingly, a need exists for an electrophotographic color image forming apparatus in which the entire developing unit does not need to be replaced when one of the color toners is exhausted.